The overall objective of this investigation was to compare and characterize the effects of carboxylic ionophore, Monensin and certain standard cardiovascular drugs on myocardial hemodynamics and coronary circulation in intact dogs. Our data demonstrates that Monensin causes dose-dependent sustained (90- less than 120 minutes) increase in cardiac contractility, blood pressue, coronary blood flow with a decrease in total peripheral resistance and minimal increase in heart rate and myocardial O2 consumption. Low doses of Monensin produce a selective increase in coronary blood flow without affecting the myocardial hemodynamics; while doses larger than 0.025 mg/Kg do affect the above mentioned cardiovascular parameters. We compared Monensin with dopamine and have concluded that Monensin may be potentially useful in the management of shock and cardiac failure. Our preliminary studies with radioactively tagged microspheres would indicate the possible effects of Monensin upon redistribution of myocardial and renal blood flows during compromised circulation. Experiments are now in progress with the use of microsphere technique in animal models of endotoxic and cardiogenic shock.